The embodiments described below relate to a power supply apparatus including a plurality of batteries capable of supplying electric power to a backupable auxiliary machine mounted in a vehicle.
Some power supply apparatuses may include a backup battery capable of supplying backup currents to a backupable auxiliary machine, such as a shift-by-wire, when a primary source of power is malfunctioning. For example, Japanese Patent Application Publication No. 2005-145097 (JP 2005-145097 A) describes a power supply apparatus including a first battery connected to a load device mounted in a vehicle and a second battery that functions as a backup power supply. According to JP 2005-145097 A, when it is determined that the state of charge (SOC) of the second battery is lower than that of the first battery, the battery connected to the load device is switched from the first battery to the second battery and the battery that functions as a backup power supply is switched from the second battery to the first battery.